It is known in the art to provide a mobile or cellular phone with a program which allows the cellular phone user to keep track of the free time remaining on their service plan within a predetermined period of time (a month, for example). Conventionally, the program requires the cellular phone user to input a value at the beginning of each month representative of the total monthly free time allotted under the service plan for communication between the cellular phone and a radio telecommunications network. The program keeps a record of the calls made by the cellular phone user within the month, and adjusts the total monthly free time value so as to generate a free time remaining value representative of the free time remaining under the service plan for the month.
The usefulness of such programs is dependent, however, upon the cellular phone user faithfully inputting the correct total monthly free time value each month. If the user inputs an incorrect total monthly free time value, then the program will provide an inaccurate estimate of the free time remaining. If the user forgets to input the total monthly free time value at the beginning of the month (or such other time as the service plan may provide for), then the user must input an estimate of the total free time remaining, or ignore the program altogether. The degree of uncertainty inherent in the user's approximation is, of course, carried over as an uncertainty in the calculated free time remaining value.